In the process, the agency’s green-eye-shade crew will have to come up with an extra $400 million for the project. That’s the delay’s cost on a mission whose price tag already is estimated at $1.88 billion before all is said and done.

The delay is the second in a year, with the project currently running about two months behind schedule.

Why the latest schedule shift? Blame it on an untimely technical glitch, a slower-than-expected assembly line for key parts (some of which were poorly made), the need to test the whole thing exhaustively, and Johannes Kepler, who first figured out how orbits worked.

It turns out that the best time to launch the mission is when the Earth and Mars are at their closest, about once every 26 months. Even if engineers could overcome the hardware problem they’ve detected in time to launch, say, in early 2010, Earth and Mars will have moved too far apart. So they have to wait another 26 months for a new launch opportunity.

With a billion-dollar price tag and an objective that aims to answer some fundamental questions about the potential for past or present life elsewhere in the solar system, NASA wants to get this mission right. The agency wants to avoid what Ed Weiler, who heads the agency’s science mission directorate, terms “a mad dash to launch.”

The Mars Science Laboratory “ranks just behind a manned mission in importance,” says Michael Griffin, NASA’s administrator. The money to pay for the delay is expected to come at the cost of delaying other science missions, officials add. First category up: Other Mars missions. Then they will turn to the planetary science community to help sort out additional options.

This is a technically complex project. The rover “dwarfs anything we’ve done before,” says Doug McCuistion, who heads the Mars Exploration Program at NASA headquaters. The “stack” — the rover, the descent stage that will ease the rover onto the surface, and the cruise stage, which keeps everything healthy en route to Mars — is largely complete, he says.

Each major element is complex enough to represent a mission in itself, he says. With all that riding to the red planet, the latest delay “was exactly the right thing to do.”